Condensation of ketenes with ketoesters



Patented Sept. 10, 1946 @ONDENSA'EION 9F KETENESWITH 1KETOESTERS John A. Spence and Edward F. .Degering, 'West Lafayette, Ind., assignors to Purdue Research Foundation, LaFayette, End, a corporation of Indiana 7 No Drawing. Application October 2, 1944,

Serial No. 556,887

'13 Claims.

This invention relates to the condensation of a ketene with a'ketoester.

Ketene is known to react with certain organic and inorganic compounds, and is known to react with itself. However, it has been generally believed thatketene would not react-witha ketone, and since the commonmethodifor preparing ketene is by the pyrolysis of a, ,ketone, viz. acetone, and-sinceno reaction occurs between the acetone and the ketene, this belief was apparentlyjustified.

Recently it has been found, however, that ketene could be condensed, in the presence of certain acid catalysts, with ketones. See the copending application of Bernard H. Gwynn and Edward Degering, Serial No.459;448, filed Septemper 23, 1942.

We have now found that ketenes can be condensed with ketocarboxylic esters toproduce unsaturated carboxylic esters. It is accordingly .an object of our invention tpprovide a process vfor preparing unsaturated-carboxylic esters. A further object is to provide newunsaturated carboxylic esters. Other objects willbecome app-arent hereinafter.

-In accordance with our invention, .we prepare unsaturated carboxylic esters by condensing .a ketene with a ketocarboxylic ester, in the presenceof an acid catalyst. Typical of the ketoesters which we employ in practicing ourinvention are the a-ketocarboxylic esters, the p-ketocarboxylic esters, the 'y-ketocarboxylic esters, the fi-ketocarboxylic esters, etc. The "ketocarboxylic ester should be one in which ther are at least two hydrogen atoms on a carbon atom or atoms adjacent to the keto carbonyl group. (It is to be noted that we employ herein the .term ketocarbonyl group to differentiate from the carbonyl group Which is in the carboxylate group of {the ketocarboxylic ester.) Preferably the :ketocarboxylic ester is one in which there are at least three hydrogen atoms on a carbon atom or atoms adj acentto one .of the keto groups, i. e. the three hydrogen .atoms can be all On one carbon atom adjacent to the :ketocarbonyl group, 'or two of the hydrogen atoms can be oncne carbon atom and the otherhydrogenatom can-benrranother carbon atom adjacent itothe ketocarbonyl group.

Among the a-ketocarboxylic esters which we employ in practicing our invention are: ethyl pyruvate, ethyl propionylformate, "ethyl n-butyrylformateoand'ethyhisovalerylformate. Among the ,p-ketocarboxylic esters which We employ in practicing our invention are: methyl acetoacetate, ethyl acetoacetate, benzyl acetoacetate,

LIX

methyl a-acetylpropionate, ethyla-acetylpropionate, methyl .a-acetylpropionate, ethylpropionoacetate, methyl .n-hutyroacetate, phenyl acetoacetate and ethyl decanoylacetate. Among the 'y-ketocarboxylic esters which we employ in practicing our invention are: methyl levulinate and ethyl levulinate. Among the o-ketocarboxylic esters: ethy1-6-(n-butyry1)=n-butyrate. Most of these ketocarboxylic esters are well known substances, the preparations of which are described in the literature. "In the case of those esters the preparation of which is not described-intheliterature, the ester can beprepared by heating the sodium salt of the corresponding acid with the appropriate organic iodide. The resulting estercan then'be extracted from the cooled reaction mixture with ether and the ester obtained from the ethereal extract.

Generally speaking the best results are-obtained with ketocarboxylicesters of the following general formula:

wherein R. represents .a hydrogen .atom, an valkyl group, an aralk ylgroup or-anaryl. group, R represents an .alkyl group, eran aralkyl group .or an aryl group, and n represents 1 2 0rd or more. With ketocarboxyliclesterslof the above formula where n has the value 3,:cyclization is likely to take place with the formation-of cyclic products. The compounds wherein .R in the iabovelgeneral formula represents hydrogen are especiall useful in: practicing ourzinvention.

Generally speakin 'two "difierent unsaturated esters fare formed whenp-ketocarboxylic :GStGIS, yeketocarboxylic testers, Beketocarboxylic esters and other ketocarboxyliclestersin which the ketccarbonyl group and carboxylate group :areseparated, are employed. Thus, with ketocarboxylic 'esters:of'therollowingsgeneralformula:

wherein Rrepresents a hydrogen atom, an alkyl group,.an aralkyl group or-an aryl group,.R' represents analkylgroup, an aralkyl group or. an aryl group and n represents .a-positive integer of 2 or more, the following two different unsaturated esters .are rf ormed-withketene wherein R, R. and n have the values given immediately above and m represents a positive integer. All of the unsaturated esters obtainable by our new process and corresponding to Formula I above are novel. With a ketene of higher molecular weight, unsaturated esters of higher molecular weight (i. e. where the acetate group in the above Formulas I and II is replaced by a higher molecular weight carboxylate group) are obtained.

On the other hand Mingasson reports having prepared the following unsaturated ester:

0000113 CH3 3=CH-C-OC2H5 by the action of acetyl chloride on the sodium salt of the enol form of acetoacetic ester. See Bull. soc. chim. (4) 45, 71 8.

. Any ketene selected from those represented by the following general formula can be employed in practicing our invention.

wherein X represents a hydroxyl group, an organic group containing a non-metal in addition to carbon and hydrogen, the X group being linked to the S atom through the said non-metallic atom, or an inorganic group consisting of nonmetallic atoms other than carbon. Sulfuric acid is an especially effective catalyst, as are chlorosulfonic acid and sulfamic acid.

In preparing the unsaturated esters of our invention, the ketocarboxylic ester is placed in a reaction vessel along with a small quantity of the acid catalyst, e. g. sulfuric acid. The mixture is the raised to reaction temperature and a ketene, preferably freshly prepared, is added to the mixture at a rate which substantially precludes the building up in the reaction mixture of any substantial quantity of unreacted ketene. The dispersion of the ketene in the reaction mixture is advantageously facilitated by agitation of the reaction mixture. Agitation also aids in avoiding local over-heating of the reaction mixture. The addition of ketene is advantageously continued until a quantity has been added which is at least as much as the molecular equivalent of the quantity of the ketocarboxylic ester present, or until no further reaction takes place.

The ketene employed in practicing our invention can be prepared in any suitable manner. A convenient method for preparing the simplest ketene (CH2=C=O) is by pyrolysis of acetone, removing the small quantity of residual acetone by passing the resulting vapors through a series of cold traps before utilizing the ketene for the condensation reaction of our invention.

The process of our invention takes place over a wide temperature range. Usually we have found that the reaction takes place at an appreciable rate at from about to about 90 C., although higher or lower temperatures can be employed. Especially with higher molecular weight ketccarboxylic esters, higher temperatures must be avoided in order to avoid thermal decomposition of the ester. The heat of reaction may require cooling of the reaction mixture to control the temperature within the desired range.

If desired a reaction medium which is inert to the ketene and the ketocarboxylic ester, e. g. a saturated aliphatic hydrocarbon, or an aromatic hydrocarbon, can be employed. However a reac tion medium is unnecessary in the case of most ketocarboxylic esters which are liquid at the reaction temperature employed.

The following examples will serve to illustrate further the manner of practicing our invention.

Example I Sixty-five parts of dried, redistilled ethyl acetoacetate (0.5 mole) were placed in a reaction vessel and .5 part (.003 mole) of concentrated sulfuric acid was added to the vessel. The temperature was raised to C. and was maintained approximately constant within :5 C. while ketene, prepared as described above, was added at a rate of between .15 to .2 mole per hour for a period of four hours during which tim the mixture wa continuously agitated. A slight amount of heat was generated by the reaction, and a slight yellow coloration appeared which gradually darkened.

The reaction mixture was distilled at 10 mm. pressure which resulted in 52 parts of a fraction boiling between and C. at that pressure. This fraction was rectified and produced 42 parts of the unsaturated acetate which boiled at 89 C. at 10 mm. pressure, corresponding to a yield based on the ethyl acetoacetate of 54%.

Analysis: Calculated for the unsaturated acetate: C, 55.30, H, 6.98. Found: C, 55.9; 56.1; H, 6.64, 7.02.

The unsaturated acetate was a mixture of two compounds having the following formulas:

. and

The latter compound constituted a very large proportion of the mixture.

Example II Sixty parts of ethyl levulinate and .5 part (.003 mole) of concentrated sulfuric acid were placed in a reaction vessel and the temperature was raised to 85 C. Ketene prepared as above described was added at a rate of about .1 mole per hour for four hours, with continuous agitation of the mixture.

The reaction mixture was rectified, yielding a 16 ml. fraction which boiled at 103-108 C. at 12 mm. The yield was 21.5% of unsaturated acetate.

Analysis: Calculated for the unsaturated acetate: C, 58.05; H, 7.57. Found: C, 57.1; 56.1; H, 7.89, 7.66.

The unsaturated acetate was a mixture of two compounds having the following formulas:

CHz=CGH2-CH2-COC2H5 and 0000113 CHa=C=C n -onioo can Both compounds were present in sizeahle proportions.

In a similar manner any of the other -letocarboxylic esters can he condensed with ketenes. Small amounts of Water may be iprescnt in any of the reaction mixtures without'adyersely affecting the process.

The proper quantity of acid employed as catalyst in these condensations will vary with the rate of addition of the keten'e, and an increased rate of addition demands a greater amount of catalyst. When operating at the most desirable rate of addition, we have found that the yield of unsaturated ester increases slowly at about the same rate as the concentration of acid is increased. When high concentrations of catalyst are employed, however, the ratio of polymeriaation of ketene to the formation of unsaturated ester increases sharply, and the yield of unsaturated ester drops off sharply.

What we claim as our invention and desire to r be secured by Letters Patent of the United States is:

1. A process for preparing an unsaturated carboxylic ester comprising condensing, in the presence of an acid catalyst selected from those represented by the following general formula:

X-SO2-OH v wherein Xrepresents a memberselected from the group consisting of a halogen atom, a hydroxyl group, and an organic group containing at least one non-metallic atom selected. from the group consisting of oxygen and nitrogen, said organic group being attached to the S atom through said non-metallic atom, .a Fketene with a ketocarboxylic ester in which there is a total of at least two hydrogen atoms on the carbon atoms adjacent to the ketocar-bonyl group.

2. A process for preparing an unsaturated carboxylic ester comprising condensing, in the presence of an acid catalyst selected from those represented by the following general formula:

wherein X represents a member selected from the group consisting of a halogen atom, a hydroxyl group, and an organic group containing at least one non-metallic atom selected from the group consisting of oxygen and nitrogen, said organic group being attached to the S atom through said non-metallic atom, a ketene with a ketocarboxylic ester in which there is a total of at least three hydrogen atoms on the carbon atoms adjacent to the ketocarbonyl group. 3. A process for preparing an unsaturated carboXylic ester comprising condensing, in the presence of an acid catalyst selected from those represented by the following general formula:

wherein X represents a member selected from the group consisting of a halogen atom, a hydroxyl group, and an organic group containing at least one non-metallic atom selected from the group consisting of oxygen and nitrogen, said organic group being attached to the S atom through said 6 non-metallic atom, a ketene with a ketocarboxylic ester selected from those represented by the following general formula:

II ll :R-CH2-C-(CH2) 1CR wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aralkyl "group and an aryl group, R represents a member selected'from the group consisting of an alkyl group, an aralkyl group and an aryl group, and n represent-s a positive integer selected from the group consisting of 1, 2 and 4.

4. A process for preparing an unsaturated carboxylic ester comprising condensing, in the presence "of sulfuric acid, a ketene with a ketocarboxylic ester selected from those represented by the following general formula:

whereiniR represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aralkyl group "and aryl group, R represents :a member selected from-the group consisting of an alkyl group, an aralkyl group and an aryl group, and n represents a positive integer selected from the group consisting of 1, 2 and 4.

5. A process for preparing anunsaturated carboxylic ester comprising condensing, in the presence of sulfamic acid, a ketene with a ketocarboxylic ester selected from those represented by the following general formula:

V RCHz( %(CH2) -1( )R' wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aralkylgroup and an aryl group, R represents a member selected from the group consisting of an alkyl group, an aralkyl group and anaryl group, and n represents a positive integer selected from the group consisting of l, 2 and 4.

"6. A process for preparing an unsaturated earboxylic ester comprising condensing, in the presence of chlorosulionic acid, a ketene with a ketocarboxylioester selected from those represented by the following general formula:

wherein R represents a member selected from the group consistin of a hydrogen atom, an alkyl group, an aralkyl group and an aryl group, R represents a member selected from th group consisting of an alkyl group, an "aralkyl group and an aryl group, and n represents a positive integer selected from the group consisting of 1, 2, and 4.

7. A process for preparing an unsaturated acetate comprising condensing, in thepresence of an acid catalyst selected from those represented by the following general formula:

wherein X represents a member selected from the group consisting of a halogen atom, a hydroxyl group, and an organic group containing at least one non-metallic atom selected from the group consisting of oxygen and nitrogen, said organic group being attached to the S atom through said non-metallic atom, ketene with a ketocarboxylic ester in which there is a total of at least two hydrogen atoms on the carbon atoms adjacent to the ketocarbonyl group.

8. A process for preparing an unsaturated acetate comprising condensing, in the presence of an acid catalyst selected from those represented by the following general formula:

group being attached to the S atom through said non-metallic atom, ketene with a keto-carboxylic ester in which there is a total of at least three hydrogen atoms on the carbon atoms adjacent to the ketocarbonyl group.

9. A process for preparing an unsaturated acetate comprising condensing, in the presence of an acid catalyst selected from those represented by the following general formula:

X-SOz-OH where X represents a member selected from the group consisting of a halogen atom, a hydroxyl group, and an organic group containin at least one non-metallic atom selected from the group consisting of oxygen and nitrogen, said organic group being attached to the S atom through said non-metallic atom, ketene with a ketocarboxylic ester selected from those represented by the following general formula:

wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aralkyl group and an aryl group, R represents a member selected from the group consisting of an alkyl group, an aralkyl group and an aryl group, and n represents a positive integer selected from the group consisting of 1, 2 and 4.

10. A process for preparing an unsaturated acetate comprising condensing, in the presence of sulfuric acid, ketene with a ketocarboxylic ester selected from those represented by the following general formula:

wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aralkyl group and an aryl group, R represents a member selected from the group consisting of an alkyl group, an aralkyl group and an aryl group, and n represents a positive integer selected from the group consisting of 1, 2 and 4.

11. A process for preparing an unsaturated acetate comprising condensing, in the presence of sulfamic acid, ketene with a ketocarboxylic ester selected from those represented by the following general formula:

wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aralkyl group and an aryl group, R represents a member selected from the group consisting of an alkyl group, an aralkyl group and an aryl group, and n represents a positive integer selected from the group consisting of 1, 2 and 4.

12. A process for preparing an unsaturated acetate comprising condensing, in the presence of chlorosulfonic acid, ketene with a ketocarboxylic ester selected from those represented by the following general formula:

wherein R represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aralkyl group and an aryl group, R represents a member selected from the group consisting of an alkyl group, an aralkyl group and an aryl group, and n represents a positive integer selected from the group consisting of 1, 2 and 4.

13. A process for preparing an unsaturated acetate comprising condensing, in the presence of sulfuric acid, keten with ethyl acetoacetate.

JOHN A. SPENCE. EDWARD F. DEGERING. 

